Proportional dehumidifier control

ABSTRACT

A water-to-air system using a modulating/proportionate control valve to regulate the amount of sensible reheat when operating in a dehumidification mode is disclosed. When in the reheat/dehumidification mode of operation, the modulating valve regulates the volume of water through a condenser coil to regulate refrigerant temperature to provide for sufficient reheating of the equipment supply air temperature within a narrow range, regardless of the inlet water temperature. The air conditioning system may be any type of water-cooled system, including a water source heat pump or water-cooled air conditioner.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 62/342,427 filed May 27, 2016, which is hereby incorporated by reference in its entirety.

BACKGROUND A. Field

This disclosure relates generally to water-to-air systems, and more particularly to a method and system of controlling a water-to-air system in dehumidification mode.

B. Description of Related Art

A water-to-air system or geothermal heat pump is a central heating and/or cooling system that transfers heat to or from the ground. When water-to-air systems are applied to areas that have excessive humidity issues, simultaneous operation of cooling mode and a reheating mode are used as a means to mitigate the indoor humidity levels, while trying not to necessarily cool or heat the conditioned space. This is referred to as a dehumidification mode of operation, because it operates like a typical dehumidifier used in a home/basement to remove excessive moisture.

One means of providing a dehumidification mode in a cooling system is referred to as a “reheat” process. In a reheat process, the supply air is reheated to a comfortable level after being cooled for adequate dehumidification. There are several known techniques to perform the reheating process, such as electric resistance heaters, de-superheating or condensing heat exchangers connected to the cooling refrigerant system, and heat exchangers connected to a boiler. The heat source in the preferred methods is some form of waste heat generated in the system as a result of the cooling process. This greatly improves the energy efficiency of the dehumidification process, as no new energy is consumed for reheat.

The simultaneous operation of both a cooling and reheating mode is an issue with these systems because the subsequent compressor discharge temperatures are much lower than an air source product. In most systems, while operating in active dehumidification mode, the reheat coil and the refrigerant-to-water coil are in direct series with one another, and the lowered discharge pressure/temperature that the refrigerant-to-water coil provides, doesn't allow for adequate heat in the indoor reheat coil to keep the supply air temperature high enough to prevent over-cooling within the conditioned space.

Thus, it would be desirable to provide a method of regulating the refrigerant temperature to maintain a neutral cooling effect while in dehumidification mode.

SUMMARY

The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope.

In one aspect, a method for controlling the dehumidification of a water-to-air system is disclosed. The water-to-air system includes water flow provided by a water source, a refrigeration circuit through which a refrigerant gas flows, and an air circuit having an inlet and an outlet. The method includes operating the water-to-air system in dehumidification mode, sensing outlet air temperature with a temperature sensor and generating a temperature signal, and reducing the water flow via a modulating valve if the temperature signal is below a predetermined set point. The refrigerant liquid changes state to a refrigerant gas after passing through an expansion device. Air passes through a reheat coil to be rewarmed prior to being exhausted through the air outlet. The reduced water flow reduces the amount of heat absorbed by water passing through the reheat coil, thereby raising the temperature of the refrigerant gas in the refrigeration circuit. Lastly, the raised temperature of the refrigerant gas passing through the reheat coil increases the amount of heat rejected into air passing through the reheat coil, thereby resulting in an increased outlet air temperature.

In another aspect, a water-to-air system is disclosed. The water-to-air system includes a water source configured to provide water to the system, a condenser connected to the water source, the condenser having a water inlet and a water outlet for receiving water from the water source, a modulating valve connected to the condenser, a compressor having a refrigerant inlet and a refrigerant outlet, an evaporator being configured to convert heat from air to refrigerant, an air circuit for circulating air in a space, the air circuit having an air inlet and an air outlet, and a temperature sensor located at the air outlet, the temperature sensor being configured to sense the outlet air temperature and generate a temperature signal. When the temperature signal is below a predetermined set point, the modulating valve reduces the water flow to the condenser, thereby raising the refrigerant condensing temperature.

In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.

FIG. 1 is a circuit diagram of a prior art water-to-air system circuit diagram;

FIG. 2 is a circuit diagram of an example water-to-air system of the present application; and

FIG. 3 is a flowchart of an example method of the operation of the water-to-air system operating in dehumidification mode according to an embodiment.

DETAILED DESCRIPTION

The present application discloses a method of controlling a water-to-air system in dehumidification mode which reduces/modulates the water flow in the refrigerant-to-water coil to raise the corresponding pressure and temperature of the discharge/outlet gas, so that a consistent supply air temperature at a neutral condition can be maintained. This can be accomplished, in one embodiment, by monitoring the supply air temperature with one or more temperature sensors only when in dehumidification mode of operation, and using its signal along with a control and modulating valve to regulate the supply air temperature to a consistent set point through the reduced water flow through the coil.

The water-to-air system of the present application comprises a water-cooled air conditioning system designed to condition the air in an enclosed space, such as a building or other structure. As used herein, “water-to-air system” denotes a system that uses a water source as a heat sink or heat source, and includes water-cooled air conditioners and water-source heat pumps, such as the system illustrated in the drawings.

Referring to FIG. 1, a typical water-to-air system 100 includes a water source 102. The water source 102 may be one of three basic types: (1) liquid circulating in a temperature-controlled piping loop with temperature control being mechanical, such as cooling towers and boilers or similar devices; (2) ground water pumped from a well, lake, river or stream; or (3) liquid circulating through a sub-surface heat exchange piping loop, which may be placed in horizontal trenches or vertical bores, or submerged within a body of surface water.

The system 100 further includes a condenser 104 that comprises a refrigerant-to-water heat exchanger or condenser/coil which is adapted to conduct heat from a refrigerant to water. As used herein, “refrigerant” denotes a suitable phase-changing heat exchange fluid for use in a vapor-compression air conditioning or heat pump system. The refrigerant condenses from a high pressure gas into a high pressure liquid once adequate heat has been removed from it within the condenser coil 104 once the refrigerant has been cooled below its adiabatic state. The refrigerant within the system is in a high pressure liquid state in the last 10-18% of the condensing coil, and in the liquid line (tubing) from the condenser coil to the inlet of an expansion device (described below). The condenser 104 contains both high pressure gas and high pressure liquid. The refrigerant enters the condenser coil as a superheated high pressure gas, is cooled to just a high pressure gas, is cooled further to where the refrigerant passes through its adiabatic state and transitions to a high pressure liquid. The liquid is then further cooled below the condensing temperature (point of adiabatic change), which is then referred to as sub-cooling. The condenser 104 has a water inlet 106 and a water outlet 108.

The system further includes an evaporator 110 comprising a refrigerant-to-air heat exchanger. Refrigerant gas circulating within the evaporator 110 (being circulated by a compressor 112) absorbs heat from the air passing through it, moved by a circulation blower 136 (which is described in more detail below). The evaporator 110 and condenser 104 are connected via a refrigerant circuit with a compressor 112 and one or more expansion devices 114, 116. The expansion devices 114, 116 may be valves or similar devices that control and regulate the amount of high pressure liquid refrigerant that is flashed-off (converted) into a low pressure gaseous refrigerant into the evaporator side of the system (dependent on the mode of operation). In other words, the refrigerant changes states from a liquid to a gas through the expansion devices 114, 116. Refrigerant on the entering side of the expansion device 114, 116 is a high pressure liquid, and on the outlet side of the expansion device is a low pressure vapor. Although two expansion devices are shown (one for heating, one for cooling), a single expansion device may be used dependent upon specific system characteristics. The compressor 112 changes the state of the low pressure superheated refrigerant gas into a high pressure superheated refrigerant gas to allow the heat to be transferred from one space into another by compressing it.

The refrigeration circuit within the water-to-air system 100 is a continuous loop that the refrigerant circulates through: compressor 112 to condenser 104 (through the discharge tubing); condenser 104 to expansion device(s) 114, 116 (through the liquid line tubing); from the expansion device(s) 114, 116 to the evaporator coil 110 (through a distributor); and from the evaporator coil 110 back to the compressor 112 (through the suction line tubing). When running in dehumidification mode, the refrigerant travels from the compressor 112 to the reheat coil 126 first, prior to going to the condenser coil 104, which is described in more detail below.

Still further, the system 100 includes an air circuit 130 for circulating air in the space (not shown) through the system 100. More specifically, the air circuit 130 is adapted to receive return air from the space at an air inlet 132, to circulate the air through the evaporator 110, across a reheat coil 126, and to direct the conditioned supply air leaving the system 100 through an air outlet 134 back into the space. The air circuit 130 usually will include one or more blowers 136 for moving the air.

The system 100 also comprises conduits (piping/tubing) adapted to circulate refrigerant between the various components of the refrigerant circuit. A dehumidification refrigerant circuit will contain a valve(s) 118 that directs the superheated gas to the refrigerant-to-air reheat coil 126 when operating in dehumidification mode. The reheat coil 126 utilizes the hot refrigerant waste heat to warm the supply air temperature to a desirable sensible neutral temperature when the system is operating in dehumidification mode. From there, the refrigerant flows to the refrigerant-to-water condenser 104 to expel the remaining waste heat.

The refrigerant circuit may further include a second valve 120 where the system comprises a heat pump. A heat pump is a reverse cycle air conditioner. Instead of extracting heat from the conditioned air space and rejecting it to the water, the refrigeration system reverses (via the reversing valve 120), and heat is extracted from the water, and is rejected to the conditioned air. The system 100 may further comprise check valves 122, 124, to ensure the refrigerant flow direction is correct, dependent upon the mode of operation.

In dehumidification mode, system 100 operates as follows: inlet air 132 from a conditioned space is drawn into the system 100, first traveling over the evaporator coil 110 which cools the air and extracts humidity due to the coil temperature being below the dew point temperature of the humidity contained in the entering air. The air is thus cooled sensibly (temperature), and latently (moisture removal). The air then passes through the reheat coil 126 to be rewarmed (sensible-temperature) prior to being exhausted back in the conditioned space 134.

The issue with the prior art system is that there is no way to balance or control the capacity differential between the evaporator coil 110, and the reheat coil 126, since indoor air temperatures and water temperatures from the water source 102 differ and change due to changing conditions, such as seasonal and daily swings. There is only a singular cross-through condition that allows for a sensible-neutral condition for the air between 132 and 134, and all other conditions with a water-to-air system typically lead to a cooling condition rather than a sensible neutral condition when operating in dehumidification mode.

As mentioned above, the system of the present application differs from that of the prior art by reducing/modulating the water flow in the refrigerant-to-water coil 104 in dehumidification mode, to raise the corresponding pressure and temperature of the refrigerant discharge gas, so that a consistent supply air temperature at a neutral condition can be maintained. In an example embodiment, shown in FIG. 2, a water-to-air system pump circuitry 200 of the present application is shown. The system 200 operates generally in a similar manner to the system 100 shown in FIG. 1.

The system 200 includes a water source 202, a refrigerant-to-water condenser/coil 204 having a water inlet 206 and a water outlet 208. The system 200 further includes an evaporator 210 comprising an air-to-refrigerant heat exchanger. The evaporator 210 is adapted to change heat from air to a refrigerant. The evaporator 210 and condenser 204 are connected via a refrigerant circuit with a compressor 212 and one or more expansion devices 214, 216, which operate in a similar manner as the compressor 112 and expansion devices 114, 116 described above with respect to FIG. 1.

Still further, the system 200 includes an air circuit 230 for circulating air in the space through the system 200. More specifically, the air circuit 230 is adapted to receive return air from the space at an air inlet 232, to circulate the air through the evaporator 210, through reheat coil 226, and to direct the conditioned supply air leaving the system 200 through an air outlet 234 back into the space. The air circuit 230 usually will include one or more blowers 236 for moving the air.

The system 200 also comprises conduits (piping/tubing) adapted to circulate refrigerant between the various components of the refrigerant circuit. A dehumidification refrigerant circuit will contain a valve 218 that directs the superheated gas to a reheat coil 226 when operating in dehumidification mode. The refrigerant circuit may include a second valve 220 where the system comprises a heat pump.

A modulating/proportionate control valve 240 is used to control the flow of water flowing through the condenser 204. The modulating valve 240 is located at the water outlet 208. In an alternate embodiment, the modulating valve 240 may be positioned at the water inlet 206. In one embodiment, the modulating valve 240 may be a modulating water flow valve which accepts multiple different inputs (0-10 Vdc (Volts Direct Current), 4-20 MA (Milli-Amps), or PWM (Pulse Width Modulation)) as a means of controlling the valve's position relative to an input signal from a control device. The mechanical portion of the modulating valve 240 may be a ball type valve, a gate type valve, or a globe type valve, for example. It should be understood that any type of known modulating valve can be used, as long as the valve has an actuator that is capable of modulating the position of the valve to modulate the water flow rate through the valve.

When supply air temperature in dehumidification mode is below the desired or specified set point, which may be adjustable by an end user, building architect, or building mechanical systems engineer, modulating valve 240 modulates or reduces water flow to raise the refrigerant condensing temperature, subsequently raising reheat coil temperature, since both the refrigerant-to-water condenser 204 and reheat condenser coils 226 are piped in series with one another. By rejecting less heat into the water condenser coil, an increased amount of heat is available to be rejected by the reheat coil 226.

With continued reference to FIG. 2, a closed loop controller or modulating valve actuator 242 is connected to the modulating valve 240. The closed loop controller/actuator 242 accepts temperature input from a supply air temperature sensor 250 and gives proportional output to regulate the modulating valve 240. The type of closed loop controller/actuator 242 used may vary with the specific input signal required by the modulating valve actuator requirements. For example, the closed loop controller 242 may comprise a proportional—integral—derivative (PID) Loop Controller or a Programmable Logic Controller (PLC). In some embodiments, the PLC of the water-to-air system may also be used for the closed loop controller 242.

The supply air temperature sensor 250 is located in the supply air discharge air stream and provides input to the loop controller via a wire 252. In alternate embodiments, the supply air temperature sensor 250 and the loop controller 252 may communicate wirelessly. The supply air temperature sensor 250 may comprise a thermocouple, a thermistor, or an RTD type probe, for example. The type of supply air temperature sensor 250 chosen is dependent upon the type of input required by the loop controller 242. The supply air temperature sensor 250 may be selected based upon specific requirements, such as, for example, the requirements of the selected loop controller 242.

A single supply air temperature sensor 250 may be used in a system having only a supply air set point, such as a system being set to modulate the valve 240 to a specific temperature, with±tolerances capabilities of all components stacked together. In another embodiment, the system 200 may include a second air temperature sensor (not shown) located at or near the air inlet 232. The second temperature sensor may be used to measure the intake air and allow the system to operate the modulating valve to a differential temperature between the two sensors, within specific±tolerances of all the combined components.

As the water flow rate through the refrigerant-to-water coil 204 is reduced, it will directly emulate a higher entering water temperature, thus raising the condensing temperature, and raising the temperature of the reheat coil, which in turn raises the discharge air temperature. This system would only be active when unit is in dehumidification mode. The modulating valve 240 would normally be driven to the full open position for standard cooling and heat pump operation.

In dehumidification mode, system 200 operates as follows: inlet air 232 from a conditioned space is drawn into the system 200, first traveling over the evaporator coil 210 which cools the air (sensible-temperature cooling), and extracts humidity (latent cooling) due to the coil temperature being below the dew point temperature of the humidity contained in the entering air. The air then passes through the reheat coil 226 to be rewarmed (sensible-temperature only) prior to being exhausted back through the air outlet 234 into the conditioned space. To regulate and control the amount of reheat supplied by the reheat coil 226, in balance with the net sensible cooling effect of the evaporator coil 210, the modulating valve 240 controls the refrigeration systems condensing temperature to control the capacity of the reheat coil 226 in balance with the sensible capacity of the evaporator coil 210.

With the reheat coil 226 and the refrigerant-to-water condenser 204 being in direct series with one another, modulating the amount of water through the refrigerant-to-water condenser 204 directly changes the capacity of the refrigerant-to-water condenser (reduced water flow=reduced heat rejection to the water), which subsequently raises the capacity available to the reheat coil 226 to balance the net sensible cooling capacity with the net sensible reheat capacity. The modulating valve 240 is controlled in measuring the outlet air 234 temperature by a temperature measurement from temperature sensor 250 fed into a logic controller 251, which then regulates the modulating valve controller/actuator 242 to control a set point of the outlet air 234.

In some embodiments, the logic controller 251 and actuator 242 can be combined into a single device dependent upon component selection. FIG. 2 shows the modulating valve 240 being located on the water outlet 208 side of the refrigerant-to-water condenser coil 204.

FIG. 3 shows a flowchart 300 detailing the method of operation of the water-to-air system of the present application. First, the system runs in dehumidification mode in step 302. As explained above, in dehumidification mode, humidity is extracted from the air. Next, the outlet air temperature is sensed using the temperature sensor 250 at step 304. The temperature sensor 250 generates a temperature signal based on the measured temperature which is transmitted to the valve controller/actuator 242 at step 306. At step 308, the water flow rate in the condenser coil 204 is reduced using the modulating valve 340 based on the temperature signal and the predetermined set point. That is, if the predetermined set point is higher than the temperature signal measured by the temperature sensor 250, then the modulating valve 340 reduces the water flow rate in the condenser 204. As the water flow rate is reduced, the condensing/refrigerant temperature is raised through a reduced capacity of the condenser coil 204 at step 310. The reduction in water flow through the condenser coil 204 reduces the amount of heat the coil is capable of rejecting into the water circulating through coil 204. Supplying additional capacity availability to the reheat coil 226 results in an increased temperature of the refrigerant gas circulating through the reheat coil 226, which produces a greater amount of heat available to be rejected. This in turn counters the cooling effect from the evaporator coil 210 more efficiently. Finally, the temperature of the air at the air outlet 234 is raised at step 312. The temperature sensor 250 continuously measures the air at the air outlet.

While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize that still further modifications, permutations, additions and sub-combinations thereof of the features of the disclosed embodiments are still possible. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope. 

1. A method for controlling the dehumidification of a water-to-air refrigeration system having water flow provided by a water source, a refrigeration circuit through which a refrigerant gas flows, and an air circuit having an inlet and an outlet, the method comprising: operating the water-to-air refrigeration system in dehumidification mode; sensing outlet air temperature via a temperature sensor and generating a temperature signal; reducing the water flow via a modulating valve if the temperature signal is below a predetermined set point; wherein air passes through a reheat coil to be rewarmed prior to being exhausted through the air outlet; wherein the reduced water flow reduces the amount of heat absorbed by water passing through the reheat coil, thereby raising the temperature of the refrigerant gas in the refrigeration circuit; and wherein the raised temperature of the refrigerant gas passing through the reheat coil increases the amount of heat rejected into air passing through the reheat coil, thereby resulting in an increased outlet air temperature.
 2. The method of claim 1 further comprising a closed loop controller configured to regulate the modulating valve based on the temperature signal.
 3. The method of claim 3 further comprising a logic controller configured to control the closed loop controller to control a set point of the outlet air.
 4. The method of claim 1 wherein the reheat coil and condenser are in direct series.
 5. The method of claim 1 wherein the predetermined set point is set by a user.
 6. The method of claim 1 wherein a second temperature sensor measures the air inlet temperature, and operates the modulating valve to a differential temperature between the two temperature sensors.
 7. A water-to-air system comprising: a water source configured to provide water to the system; a condenser connected to the water source, the condenser having a water inlet and a water outlet for receiving water from the water source; a modulating valve connected to the condenser; a compressor having a refrigerant inlet and a refrigerant outlet; an evaporator being configured to convert heat from air to refrigerant; an air circuit for circulating air in a space, the air circuit having an air inlet and an air outlet; and a temperature sensor located at the air outlet, the temperature sensor being configured to sense the outlet air temperature and generate a temperature signal; wherein when the temperature signal is below a predetermined set point, the modulating valve reduces the water flow to the condenser, thereby raising the refrigerant condensing temperature.
 8. The system of claim 7 wherein the modulating valve is located at the water outlet.
 9. The system of claim 7 wherein the modulating valve is located at the water inlet.
 10. The system of claim 7 further comprising a second temperature sensor located at or near the air inlet. 